The present invention relates to a fuel supply pump of an internal combustion engine.
A common-rail fuel injection system is applied for internal combustion engines such as diesel engine and other similar engines.
The common-rail fuel injection system is equipped with a common rail that accumulates high-pressure fuel and a fuel supply pump that supplies the high-pressure fuel to the common rail. In response to a command from an engine control unit (ECU), the high-pressure fuel in the common rail is injected and supplied through a fuel injection valve to each cylinder of the internal combustion engine at a predetermined period.
An example of conventional fuel supply pumps is disclosed in Japanese Patent Publication H11-315767.
A fuel supply pump 100, as shown in FIG. 5, is provided with a low-pressure feed pump 101 and a pump element. The pump element is composed of a cylinder 109, a plunger 102 contained in the cylinder to be reciprocable in the axial direction, and a compressing chamber 106 formed among inner peripheral surfaces of one end portion of the cylinder 109 and one end surface of the plunger 102.
The fuel supply pump 100 is also provided with a plunger driving unit including a driving shaft 103, a cam 110 mechanically connected to the driving shaft 103 and to the plunger 102, and a pump-cam chamber 111 in which a part of the driving shaft 103 and the cam 110 are contained.
The driving shaft 103 is rotated so that the cam 110 converts the rotation of the driving shaft 103 to reciprocation, and transfers the reciprocation to the plunger 102, whereby the plunger 102 reciprocally moves in the axial direction in the cylinder 109.
The fuel supply pump 100 is further provided with a control valve 107, a check valve 104, a lubricating path 105, and a fuel tank 118.
The fuel accumulated in the fuel tank 118 is supplied by the pump operation of the low-pressure feed pump 101 through the fuel supply path 108 to the compressing chamber 106. The fuel in the compressing chamber 106 is compressed by the reciprocation of the plunger 102 by the plunger-driving unit to be highly pressurized, so that the high-pressurized fuel is supplied to a common rain (not shown).
In addition, a part of the fuel delivered from the low-pressure feed pump 101 is supplied through the lubricating path 105 to the pump-cam chamber 111 so that the slide portions of the pump element are cooled and lubricated.
A fuel flow path connected between the outlet of the low-pressure feed pump 101 and the cylinder 109 to be communicated with the compressing chamber 106 is provided with the control valve 107. The control valve 107 is operative to control the flow rate of the fuel supplied from the low-pressure pump 101 to the compressing chamber 106, thereby controlling the fuel amount supplied to the common rail. This fuel-amount control operation is carried out in response to a command from the ECU to keep the fuel pressure in the common rail at a predetermined pressure. A fuel supply path 108 connected between the control valve 107 and the cylinder 109 to be communicated with the compressing chamber 106 is provided with the check valve 104 that prevents the high-pressurized fuel from flowing backward from the compressing chamber 106 to the control valve 107.
In the conventional configuration of the fuel supply pump 100, even when the ECU sends a command to the control valve 107 to decrease the fuel amount supplied to the common rail, excessive fuel may pass through the control valve 107 into the fuel supply path 108. This overflow is caused by the leakage of fuel from the valve portion of the control valve 107 and/or the delay in the closing of the valve member thereof.
This excessive fuel may be supplied through the fuel supply path 108 to the compressing chamber 106.
Then, in order to relieve the excessive fuel in the fuel supply path 108, a fuel relief path 112 is branched from the fuel supply path 108 to bypass the pump element, and connected to the inlet of the low-pressure feed pump 101.
However, the control valve 107 and the inlet of the low-pressure pump 101 are far from each other, so that the fuel relief path 112 increases in length. In addition, as shown in FIG. 5, because the fuel relief path 112 bypasses the feed pump 101, the fuel relief path 112 is bent at its many mid-points, which causes the form of the fuel relief path 112 to be complicated. This results in deteriorating the workability of fuel relief path 112.